System and method for adaptive switching frequency control

ABSTRACT

System and method for providing frequency control to a power converter. The system includes a controller configured to receive a load signal and generate a first control signal. The load signal indicates an output load for a power converter. Additionally, the system includes a signal generator configured to receive the first control signal and generates at least a first output signal. The first output signal is associated with a first signal strength and a first frequency. The first frequency is inversely proportional to a sum of a first time period, a second time period, and a third time period. The first signal strength increases with the time during the first time period, the first signal strength decreases with the time during the second time period, and the first signal strength is constant with respect to the time during the third time period.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.200510024385.6 (EastIP Ref. No. 05NI2016-1365-SMY), filed Mar. 11, 2005,entitled “System and Method for Adaptive Switching Frequency Control,”by Inventors Jun Ye, Zhen Zhu, Shifeng Zhao, Lieyi Fang, and ZhiliangChen, commonly assigned, incorporated by reference herein for allpurposes.

The following two commonly-owned co-pending applications, including thisone, are being filed concurrently and the other one is herebyincorporated by reference in its entirety for all purposes:

1. U.S. patent application Ser. No. ______, in the name of Jun Ye, ZhenZhu, Shifeng Zhao, Lieyi Fang, and Zhiliang Chen, titled, “System andMethod for Adaptive Switching Frequency Control,” (Attorney DocketNumber 025748-000200US); and

2. U.S. patent application Ser. No. ______, in the name of Jun Ye, ZhenZhu, Shifeng Zhao, Lieyi Fang, and Zhiliang Chen, titled, “System andMethod for Controlling Variations of Switching Frequency,” (AttorneyDocket Number 025748-000300US).

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

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REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK.

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BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for frequencycontrol. Merely by way of example, the invention has been applied to apower converter. But it would be recognized that the invention has amuch broader range of applicability.

Power converters are widely used for consumer electronics such asportable devices. The power converters can convert electric power fromone form to another form. As an example, the electric power istransformed from alternate current (AC) to direct current (DC), from DCto AC, from AC to AC, or from DC to DC. Additionally, the powerconverters can convert the electric power from one voltage level toanother voltage level. The power converters include linear convertersand switch-mode converters.

The switch-mode converters can consume significant power under standbyconditions. For example, the standby conditions correspond to light orzero output loads. The standby power includes energy losses at variouscomponents of the switch-mode converters such as power switches,transformers, inductors, and snubbers. These losses often increase withthe switching frequency. To reduce the standby power, the switchingfrequency is usually lowered for light or zero output loads. FIG. 1 is aconventional diagram for switching frequency control. When the controlvoltage is lower than a threshold voltage, the switching frequency issmaller than the normal frequency. The control voltage increases withthe output load.

Some conventional switch-mode converters use an oscillator to generate aswitching frequency. The switching frequency is modulated based on themagnitude of an output load. For example, the oscillator includes aramping waveform generator or an RC oscillator if the normal frequencyis in the range of tens of kHz. The rising time is controlled by acurrent source to charge a capacitor, and the falling time is controlledby a current sink to discharge the capacitor. By controlling the chargeand/or discharge current of the capacitor, the switching frequency ismodulated. But this conventional technique often cannot providesufficient stability to the switch-mode converters.

Hence it is highly desirable to improve techniques for switchingfrequency control.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for frequencycontrol. Merely by way of example, the invention has been applied to apower converter. But it would be recognized that the invention has amuch broader range of applicability.

According to one embodiment of the present invention, a system forproviding frequency control to a power converter is provided. The systemincludes a controller configured to receive a load signal and generate afirst control signal. The load signal indicates an output load for apower converter. Additionally, the system includes a signal generatorconfigured to receive the first control signal and generates at least afirst output signal. The first output signal is associated with a firstsignal strength and a first frequency. The first frequency is inverselyproportional to a sum of a first time period, a second time period, anda third time period. The first signal strength increases with the timeduring the first time period, the first signal strength decreases withthe time during the second time period, and the first signal strength isconstant with respect to the time during the third time period. Thethird time period varies with the load signal if the load signal iswithin a predetermined range.

According to another embodiment, a system for providing frequencycontrol to a power converter includes a first controller configured toreceive a load signal and generate a first control signal. The loadsignal indicates an output load for a power converter. Additionally, thesystem includes a compensation system configured to receive an inputsignal for the power converter and generate a second control signal, anda signal generator configured to receive the first control signal andthe second control signal and generates at least an output signal. Theoutput signal is associated with a signal strength and a frequency. Thefrequency is inversely proportional to a sum of a first time period, asecond time period, and a third time period. The signal strengthincreases with the time at a first slope during the first time period,the signal strength decreases with the time at a second slope during thesecond time period, and the signal strength is constant with respect tothe time during the third time period. The first slope varies with theinput signal within a signal range, and the second slope varies with theinput signal within the signal range.

According to yet another embodiment, a method for providing frequencycontrol to a power converter includes receiving a load signal. The loadsignal indicates an output load for a power converter. Additionally, themethod includes generating a control signal in response to the loadsignal, processing information associated with the control signal, andgenerating an output signal based on at least information associatedwith the control signal. The output signal is associated with a signalstrength and a frequency. The frequency is inversely proportional to asum of a first time period, a second time period, and a third timeperiod. The signal strength increase with the time during the first timeperiod, the signal strength decrease with the time during the secondtime period, and the signal strength is constant with respect to thetime during the third time period. The third time period varies with theload signal if the load signal is within a predetermined range.

According to yet another embodiment, a method for providing frequencycontrol to a power converter includes receiving a load signal. The loadsignal indicates an output load for a power converter. Additionally, themethod includes generating a first control signal in response to theload signal, receiving an input signal for the power converter,generating a second control signal in response to the input signal,processing information associated with the first control signal and thesecond control signal, and generating an output signal based on at leastinformation associated with the first control signal and the secondcontrol signal. The output signal is associated with a signal strengthand a frequency. The frequency is inversely proportional to a sum of afirst time period, a second time period, and a third time period. Thesignal strength increases with the time at a first slope during thefirst time period, the signal strength decreases with the time at asecond slope during the second time period, and the signal strength isconstant with respect to the time during the third time period. Thefirst slope varies with the input signal within a signal range, and thesecond slope varies with the input signal within the signal range.

Many benefits are achieved by way of the present invention overconventional techniques. For example, some embodiments of the presentinvention provide an adaptive signal generator. The signal frequency iscontrolled by at least a control signal generated by a frequencyvariation generator and another control signal that represents theoutput loading. For example, the frequency variation generator outputs arandomized signal. In another example, the control signal for outputloading includes a feedback voltage. Certain embodiments of the presentinvention provide an efficient control over switching frequency with lowstandby power. Some embodiments of the present invention improvestability of the power converter.

Certain embodiments of the present invention use dead-time modulationfor adaptive frequency control. Some embodiments of the presentinvention provide an output waveform that includes three phases. In oneembodiment, the three phases include a charging phase, a dischargingphase, and a dead-time phase. For example, a dead-time phase is insertedbetween a discharging phase and a charging phase. In anther embodiment,the oscillator output frequency is adjusted by modulating the dead-timephase in response to various load conditions. For example, the dead-timephase is modulated by a voltage representing the output load for aswitch-mode power converter. In yet another embodiment, the time periodfor the charging phase and the time period for the discharging phase areboth independent of the load conditions. In yet another embodiment, theslope for signal strength during the charging phase and the dischargingphase is independent of the load conditions. For example, the slopedepends on the input voltage of the switch-mode power converter, but notthe output load of the switch-mode power converter. Certain embodimentsof the present invention provide dead-time modulation by charging acapacitor from an initial voltage level to a threshold voltage levelwith a constant current source. Some embodiments of the presentinvention provide a dead-time phase whose time period increases with theoutput load under light load or no load conditions. Some embodiments ofthe present invention provide a dead-time phase whose time period equalto zero under normal and heavy load conditions.

Certain embodiments of the present invention provide a signal generator.The signal slope is compensated for variations in input voltage, andused for slop compensation in a switch-mode power converter. Forexample, the power converter operates in the current mode. Someembodiments of the present invention sense the input voltage and adjustat least the charging and discharging currents accordingly. Certainembodiments of the present invention provide a ramping signal used forslope compensation. The ratio of slope compensation remains constantwith respect to the input voltage. Some embodiments of the presentinvention improve stability of current feedback loop. Certainembodiments of the present invention use a clock randomizer forfrequency modulation.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and the accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conventional diagram for switching frequency control;

FIG. 2 is a simplified system for frequency control according to anembodiment of the present invention;

FIG. 3 is a simplified diagram for frequency control with dead-timemodulation according to an embodiment of the present invention;

FIG. 4 is a simplified compensator according to an embodiment of thepresent invention;

FIG. 5 is a simplified diagram for slope control according to anembodiment of the present invention;

FIG. 6 is a simplified diagram for clock signal and ramping signalaccording to an embodiment of the present invention;

FIG. 7 is a simplified frequency variation generator according to anembodiment of the present invention;

FIG. 8 is a simplified system for frequency control according to anotherembodiment of the present invention;

FIG. 9 is a simplified diagram for a compensator and current sourcesaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a system and method for frequencycontrol. Merely by way of example, the invention has been applied to apower converter. But it would be recognized that the invention has amuch broader range of applicability.

FIG. 2 is a simplified system for frequency control according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. A system 200 includes a frequency variation generator210, a compensator 220, a dead-time controller 230, a signal generator240, and a pulse-width-modulation (PWM) generator 250. Although theabove has been shown using a selected group of components for the system200, there can be many alternatives, modifications, and variations. Forexample, some of the components may be expanded and/or combined. Othercomponents may be inserted to those noted above. Depending upon theembodiment, the arrangement of components may be interchanged withothers replaced. For example, the PWM generator 250 is replaced byanother component receiving at least an output signal of the signalgenerator 240. In another example, the compensator 220 is a compensationsystem. Further details of these components are found throughout thepresent specification and more particularly below.

The signal generator 240 receives control signals 212, 222, and 232 fromthe frequency variation generator 210, the compensator 220, and thedead-time controller 230 respectively. In response, the signal generator240 outputs a clock signal 242 and a ramping signal 244 to the PWMgenerator 250. In one embodiment, the PWM generator 250 also receives avoltage feedback signal 252 and a current sensing signal 254, andgenerates a PWM signal 256. For example, the PWM signal 256 is used toturn on or off a power switch in a switch-mode power converter. In oneembodiment, the switch-mode power converter is an off-line powerconverter. In another example, the ramping signal 244 is used for slopcompensation in the switch-mode power converter. In one embodiment, thepower converter operates in a current mode. In another embodiment, thesignal generator includes an oscillator.

The dead-time controller 230 receives a load signal 234 and generatesthe control signal 232. The load signal 234 represents the level ofoutput load for the switch-mode converter. For example, the load signal234 includes a control voltage which increases with the output load. Asanother example, the load signal 234 is generated by a feedback loop. Inresponse to the load signal 234, the dead-time controller 230 outputsthe control signal 232 to the signal generator 240. The signal generator240 uses the control signal 232 to perform frequency control.

FIG. 3 is a simplified diagram for frequency control with dead-timemodulation according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 3, curves310 and 320 represent the ramping signal 244 generated by the signalgenerator 240. Each curve has a vertical axis representing signalstrength and a horizontal axis representing time. For example, thevertical axis indicates voltage level or current level. The curve 310 isthe ramping signal 244 without any dead-time modulation. Each periodincludes a charging time T_(on) and a discharging time T_(off). Thecurve 320 is the ramping signal 244 with dead-time modulation. Forexample, A dead-time phase is inserted to successive discharging andcharging phases. Each period includes a charging time T_(on), adischarging time T_(off), and a dead time T_(dead). During T_(dead), thesignal strength remains constant with time. If T_(dead) equals zero, thecurve 320 becomes the same as the curve 310.

In one embodiment, T_(dead) is modulated by the load signal 234 throughthe dead-time controller 230. For example, under light or no loadconditions, a long T_(dead) is generated. In another example, undernormal and heavy load condition, a T_(dead) substantially equal to zerois generated. In another embodiment, the frequency of the ramping signal244 is controlled by the output load of the switch-mode converter.

The compensator 220 receives an input voltage 224 and generates thecontrol signal 222. The control signal 222 is received by the signalgenerator 240. For example, the signal generator 240 includes anoscillator. In another example, the signal generator outputs the rampingsignal whose slope of signal strength as a function of time is adjustedbased on the control signal 222.

FIG. 4 is a simplified compensator according to an embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thecompensator 220 includes a sensing system 410 and a compensationcontroller 420. The sensing system 410 receives the input voltage 224and generates a control signal 430. The control signal 430 representsthe magnitude of the input voltage 224. In one embodiment, the controlsignal 430 is in the current domain. In another embodiment, the controlsignal 430 is in the voltage domain. The control signal 430 is receivedby the compensation controller 420, which generates the control signal222 in response.

As discussed above, the control signal 222 is received by the signalgenerator 240. For example, the signal generator 240 includes anoscillator. In another example, the signal generator 240 outputs theramping signal 244 whose slope of signal strength as a function of timeis adjusted based on the control signal 222. FIG. 5 is a simplifieddiagram for slope control according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 5, curves 510 and 520 represent the ramping signal 244 generated bythe signal generator 240. Each curve has a vertical axis representingsignal strength and a horizontal axis representing time. For example,the vertical axis indicates voltage level or current level. The curves510 and 520 has the same frequency. Each period includes a charging timeT_(on), a discharging time T_(off), and a dead time T_(dead). DuringT_(on) and T_(off), the slope of the curve 510 has a magnitude smallerthan that of the curve 520. During T_(dead), the slopes of the curves510 and 520 are the same and equal to zero. In one embodiment, the curve510 corresponds to a voltage level V₁ for the input voltage 224, and thecurve 520 corresponds to a voltage level V₂ for the input voltage 224.For example, V₁ is larger than V₂. In another embodiment, slope of theramping signal 244 vary with the input voltage 224 during charging anddischarging periods. The slope is used by the switch-mode powerconverter to provide slope compensation to the feedback loop. Forexample, the slope compensation ratio is constant regardless of theinput voltage 224. In another example, the power converter operates inthe current mode.

Additionally, as shown in FIG. 2, the signal generator 240 outputs theclock signal 242. For example, the clock signal 242 has the samefrequency as the ramping signal 244. In another example, the clocksignal 242 is used by the PWM generator 250 to control switchingfrequency of the switch-mode power converter.

FIG. 6 is a simplified diagram for clock signal and ramping signalaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 6, curves960 and 970 represent the clock signal 242 and the ramping signal 244respectively. The curves 960 and 970 each have a vertical axisrepresenting signal strength and a horizontal axis representing time.For example, the vertical axis indicates voltage level or current level.In one embodiment, the curve 970 is the same as the curve 320.

The curves 960 includes two phases T_(CL) and T_(CH) for each period.The phase T_(CL) corresponds to a low clock signal strength, and thephase T_(CL) corresponds to a clock high signal strength. The curves 970includes three phases T_(on), T_(off), and T_(dead). T_(on) is equal toT_(CL), and the sum of T_(off) and T_(dead) is equal to T_(CH). The sumof T_(CL) and T_(CH) equals the sum of T_(on), T_(off), and T_(dead).The curves 960 and 970 have the same frequency.

Returning to FIG. 2, the frequency variation generator 210 generates thecontrol signal 212. The control signal 212 is used by the signalgenerator 240 to provide a frequency spread to the signal generated byan oscillator of the signal generator 240. FIG. 7 is a simplifiedfrequency variation generator according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. Thefrequency variation generator 210 is a clock randomizer. The clockrandomizer includes an m-stage M-sequence generator 610 and an N-bitdigital-to-analog converter 620. The N-bit digital-to-analog converter620 receives a signal 630 and generates the control signal 212. Forexample, the control signal 212 is a pseudo random signal. In anotherembodiment, the frequency variation generator 210 includes a systemcapable of providing frequency variations. See U.S. Pat. Nos. 6,229,366and 6,249,876.

FIG. 8 is a simplified system for frequency control according to anotherembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. A system 700 includes a frequency variation generator710, a compensator 720, switches 730, 732 and 734, NANDs 740 and 742,AND 744, comparators 750, 752 and 754, inverters 760 and 762, capacitors770 and 772, current sources 780, 782, 784, 786 and 788. Although theabove has been shown using a selected group of components for the system700, there can be many alternatives, modifications, and variations. Forexample, some of the components may be expanded and/or combined. Othercomponents may be inserted to those noted above. Depending upon theembodiment, the arrangement of components may be interchanged withothers replaced. Further details of these components are foundthroughout the present specification and more particularly below.

The capacitor 770 is charged or discharged through the switch 730 (SH)or the switch 732 (SL) respectively. Between the discharging phase(T_(off)) and the charging phase (T_(on)), a dead time T_(dead) can beinserted between T_(on) and T_(off) by keeping both switches 730 and 732open. The outputs of comparators 750 (A1) and 752 (A2) are latched by anRS flip-flop. The RS flip-flop includes the NANDs 740 (NAND1) and 742(NAND2). The comparators 750 (A1) and 752 (A2) are voltage clampingcomparators with threshold voltages 840 (V_(H)) and 842 (V_(L))respectively. The voltage 830 at one terminal of the capacitor 770 has avoltage range that is equal to the difference between the thresholdvoltages 842 and 840.

The capacitor 772 (C_(g)), the current source 784 (I_(g)), the switch734 (SG), and the comparator 754 (A3) are used for dead-time modulation.If a control voltage 810 (V_(ctrl)) is smaller than a threshold voltage(V_(th) _(—) _(g)), a voltage 814 at one terminal of the capacitor 772begins to rise from the control voltage 810 to the threshold voltage 812after a discharging phase (T_(off)) ends for the capacitor 770 (C₀). Forexample, the rise of the voltage 814 is supported by the current source784. At the end of the discharging period, the switch 734 becomes open.

When the voltage 814 reaches the threshold voltage 812, a signal 820generated by the AND 744 (AND1) is used to close the switch 730 (SH).Subsequently, the voltage 830 for the capacitor 770 starts to rise, andthe charging phase (T_(on)) begins. In one embodiment, the dead timeT_(dead) is the period when the switches 730 and 732 are both open.During the dead time, the voltage 830 is kept constant.

As shown in FIG. 8, the dead time T_(dead) is proportional to thedifference between the threshold voltage (V_(th) _(—) _(g)) and thecontrol voltage 810 (V_(ctrl)) if V_(ctrl) is less than V_(th) _(—)_(g). For example, T_(dead) increases with decreasing V_(ctrl) ifV_(ctrl) is less than V_(th) _(—) _(g). The oscillation frequency of thevoltage 830 decreases with decreasing V_(ctrl). For example, the controlvoltage 810 (V_(ctrl)) represents the level of output load for theswitch-mode converter. In another example, V_(ctrl) increases with theoutput load. In yet another example, V_(ctrl) is generated by a feedbackloop. If V_(ctrl) is greater than or equal to V_(th) _(—) _(g), the deadtime T_(dead) equals to zero.

In another embodiment, V_(th) _(—) _(g) corresponds a threshold outputload, and V_(ctrl) varies with the output load. For example, V_(ctrl)increases with the output load. As shown in FIG. 8, T_(dead) increaseswith the decreasing output load if the output load is less than thethreshold output load. For example, T_(dead) increases with thedecreasing output load if the output load is less than the thresholdoutput load but more than another threshold output load. If the outputload is more than or equal to the threshold output load, the dead timeT_(dead) equals to zero.

In yet another embodiment, the charging time T_(on) and the dischargingtime T_(off) each are constant with respect to V_(ctrl). For example,V_(ctrl) varies with the output load. The charging time T_(on) and thedischarging time T_(off) each are constant with respect to output load.

In yet another embodiment, time periods for charging phase, dischargingphase, and dead time phase are determined as follows: $\begin{matrix}{T_{on} = \frac{\left( {V_{H} - V_{L}} \right) \times C_{O}}{I_{C} + I_{CM}}} & \left( {{Equation}\quad 1} \right) \\{T_{off} = \frac{\left( {V_{H} - V_{L}} \right) \times C_{O}}{I_{D} + I_{DM}}} & \left( {{Equation}\quad 2} \right) \\{T_{dead} = {{\frac{\left( {V_{th\_ g} - V_{ctrl}} \right) \times C_{g}}{I_{g}}\quad{if}\quad V_{th\_ g}} > V_{ctrl}}} & \left( {{Equation}\quad 3} \right) \\{T_{dead} = {{0\quad{if}\quad V_{th\_ g}} \leq V_{ctrl}}} & \left( {{Equation}\quad 4} \right)\end{matrix}$

where T_(on), T_(off) and T_(dead) are time periods for charging phase,discharging phase, and dead-time phase respectively. T_(on) depends onthe sum of current sources 780 (I_(C)) and 786 (I_(CM)) and thedifference between the threshold voltages 840 (V_(H)) and 842 (V_(L)).T_(off) depends on the sum of current sources 782 (I_(D)) and 788(I_(DM)) Additionally, the frequency F_(S) of the voltage 830 is definedas follows: $\begin{matrix}{F_{S} = \frac{1}{T_{on} + T_{off} + T_{dead}}} & \left( {{Equation}\quad 5} \right)\end{matrix}$

As shown in FIG. 8, the current sources 786 (I_(CM)) and 788 (I_(DM))are modulated by control signals 1860 and 1862 from the frequencyvariation generator 710. In one embodiment, the frequency variationgenerator 710 includes the m-stage M-sequence generator 610 and theN-bit digital-to-analog converter 620 as shown in FIG. 7. In anotherembodiment, the frequency variation generator 710 includes a systemcapable of providing frequency variations. See U.S. Pat. Nos. 6,229,366and 6,249,876.

The current sources 780 (I_(C)) and 782 (I_(D)), and the thresholdvoltages 840 (V_(H)) and 842 (V_(L)) are modulated by the compensator720. The compensator 720 receives an input voltage 850. FIG. 9 is asimplified diagram for a compensator and current sources according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. The system 900 includes a transconductor 910, a resistor912, current sources 920 and 922, and voltage sources 930 and 932.Although the above has been shown using a selected group of componentsfor the system 900, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above.Depending upon the embodiment, the arrangement of components may beinterchanged with others replaced. Further details of these componentsare found throughout the present specification and more particularlybelow.

The transconductor 910 receives an input voltage 914 and generatescurrents 940 (I₀₁) and 942 (I₀₂). The currents 940 and 942 are receivedby the current sources 920 and 922 respectively, which output thecurrents I_(C) and I_(D) respectively. For example,I _(C) =I _(C0) −I ₀₁  (Equation 6)I _(D) =I _(D0) −I ₀₂  (Equation 7)

In one embodiment, $\begin{matrix}{\frac{I_{C\quad 0}}{I_{D\quad 0}} = \frac{I_{01}}{I_{02}}} & \left( {{Equation}\quad 8} \right)\end{matrix}$

Additionally, the transconductor 910 generates a voltage 944 (V₀)through the resistor 912 in response to the input voltage 914. Thevoltage 944 is received by the voltage sources 930 and 932, which outputthe voltages V_(H) and V_(L) respectively. For example,V _(H) =V _(H0) −V ₀  (Equation 9)V _(L) =V _(L0) −V ₀  (Equation 10)

In one embodiment, the system 914 is used as the compensator 720 and thecurrent sources 780 and 782. The currents I_(C) and I_(D) are used forcharging and discharging of the capacitor 770 respectively. The voltagesV_(H) and V_(L) are used as threshold voltages for comparators 750 and752 respectively.

As shown in FIGS. 8 and 9, the voltage 830 increases with time at aslope during the charging phase (T_(on)), and decreases with time atanother slope during the discharging phase (T_(off)). Both slopes varywith the input voltage 850. For example, the slopes vary with the inputvoltage 850 within a predetermined voltage range. In another example,the slopes are constant with respect to the control voltage 810(V_(ctrl)), but vary with respect to the input voltage 850.

As discussed above and further emphasized here, FIG. 8 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. In one embodiment, the voltage 830 is used as aramping signal, and the signal 820 is used as a clock signal. Forexample, the ramping signal and the clock signal are received by a PWMgenerator. The PWM generator uses the ramping signal to provide slopecompensation. For example, the slope compensation ratio is constantregardless of the input voltage 850. Additionally, the PWM generatoruses the clock signal to control switching frequency.

In another embodiment, the system 700 is used as the system 200. Forexample, the voltage 830 is the ramping signal 244, and the signal 820is the clock signal 242. In another example, the frequency variationgenerator 710 is the frequency variation generator 210. In yet anotherexample, the compensator 720 is the compensator 220. In yet anotherexample, the control voltage 810 is the load signal 234. In yet anotherexample, the input voltage 850 is the input voltage 224. In yet anotherembodiment, the system 200 or 700 is a part of the power converter.

In yet another embodiment, a method for providing frequency control to apower converter includes receiving a load signal. The load signalindicates an output load for a power converter. Additionally, the methodincludes generating a control signal in response to the load signal,processing information associated with the control signal, andgenerating an output signal based on at least information associatedwith the control signal. The output signal is associated with a signalstrength and a frequency. The frequency is inversely proportional to asum of a first time period, a second time period, and a third timeperiod. The signal strength increase with the time during the first timeperiod, the signal strength decrease with the time during the secondtime period, and the signal strength is constant with respect to thetime during the third time period. The third time period varies with theload signal if the load signal is within a predetermined range. Forexample, the method can be performed by the system 200 and/or the system700.

In yet another embodiment, a method for providing frequency control to apower converter includes receiving a load signal. The load signalindicates an output load for a power converter. Additionally, the methodincludes generating a first control signal in response to the loadsignal, receiving an input signal for the power converter, generating asecond control signal in response to the input signal, processinginformation associated with the first control signal and the secondcontrol signal, and generating an output signal based on at leastinformation associated with the first control signal and the secondcontrol signal. The output signal is associated with a signal strengthand a frequency. The frequency is inversely proportional to a sum of afirst time period, a second time period, and a third time period. Thesignal strength increases with the time at a first slope during thefirst time period, the signal strength decreases with the time at asecond slope during the second time period, and the signal strength isconstant with respect to the time during the third time period. Thefirst slope varies with the input signal within a signal range, and thesecond slope varies with the input signal within the signal range. Forexample, the method can be performed by the system 200 and/or the system700.

The present invention has various advantages. Some embodiments of thepresent invention provide an adaptive signal generator. The signalfrequency is controlled by at least a control signal generated by afrequency variation generator and another control signal that representsthe output loading. For example, the frequency variation generatoroutputs a randomized signal. In another example, the control signal foroutput loading includes a feedback voltage. Certain embodiments of thepresent invention provide an efficient control over switching frequencywith low standby power. Some embodiments of the present inventionimprove stability of the power converter.

Certain embodiments of the present invention use dead-time modulationfor adaptive frequency control. Some embodiments of the presentinvention provide an output waveform that includes three phases. In oneembodiment, the three phases include a charging phase, a dischargingphase, and a dead-time phase. For example, a dead-time phase is insertedbetween a discharging phase and a charging phase. In anther embodiment,the oscillator output frequency is adjusted by modulating the dead-timephase in response to various load conditions. For example, the dead-timephase is modulated by a voltage representing the output load for aswitch-mode power converter. In yet another embodiment, the time periodfor the charging phase and the time period for the discharging phase areboth independent of the load conditions. In yet another embodiment, theslope for signal strength during the charging phase and the dischargingphase is independent of the load conditions. For example, the slopedepends on the input voltage of the switch-mode power converter, but notthe output load of the switch-mode power converter. Certain embodimentsof the present invention provide dead-time modulation by charging acapacitor from an initial voltage level to a threshold voltage levelwith a constant current source. Some embodiments of the presentinvention provide a dead-time phase whose time period increases with theoutput load under light load or no load conditions. Some embodiments ofthe present invention provide a dead-time phase whose time period equalto zero under normal and heavy load conditions.

Certain embodiments of the present invention provide a signal generator.The signal slope is compensated for variations in input voltage, andused for slop compensation in a switch-mode power converter. Forexample, the power converter operates in the current mode. Someembodiments of the present invention sense the input voltage and adjustat least the charging and discharging currents accordingly. Certainembodiments of the present invention provide a ramping signal used forslope compensation. The ratio of slope compensation remains constantwith respect to the input voltage. Some embodiments of the presentinvention improve stability of current feedback loop. Certainembodiments of the present invention use a clock randomizer forfrequency modulation.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1. A system for providing frequency control to a power converter, thesystem comprising: a controller configured to receive a load signal andgenerate a first control signal, the load signal indicating an outputload for a power converter; a signal generator configured to receive thefirst control signal and generates at least a first output signal;wherein: the first output signal is associated with a first signalstrength and a first frequency; the first frequency is inverselyproportional to a sum of a first time period, a second time period, anda third time period; the first signal strength increases with the timeduring the first time period; the first signal strength decreases withthe time during the second time period; the first signal strength isconstant with respect to the time during the third time period; thethird time period varies with the load signal if the load signal iswithin a predetermined range.
 2. The system of claim 1 wherein the thirdtime period varies with the load signal if the load signal is within apredetermined range comprises: if the output load is less than athreshold load, the third time period increases with the decreasingoutput load.
 3. The system of claim 1 wherein the third time periodequals zero if the load signal is not within the predetermined range. 4.The system of claim 3 wherein the third time period equals zero if theload signal is not within the predetermined range comprises: if theoutput load is more than or equal to a threshold load, the third timeperiod equals zero.
 5. The system of claim 1 wherein the first timeperiod is constant with respect to the load signal, and the second timeperiod is constant with respect to the load signal.
 6. The system ofclaim 1 wherein: the signal generator is further configured to generatea second output signal associated with a second signal strength and asecond frequency; the second frequency is inversely proportional to afourth time period and a fifth time period; the second signal strengthduring the fourth time period is different from the second signalstrength during the fifth time period.
 7. The system of claim 6 whereinthe first frequency is equal to the second frequency.
 8. The system ofclaim 7 wherein the fourth period is equal to the first period, and thefifth period is equal to a sum of the second period and the thirdperiod.
 9. The system of claim 7, and further comprising apulse-width-modulation generator configured to receive at least thesecond output signal.
 10. The system of claim 9 wherein thepulse-width-modulation generator uses the second signal to control aswitching frequency for the power converter.
 11. The system of claim 1wherein the controller comprises a first capacitor associated with afirst voltage; wherein: the load signal represents a load voltage level,the load voltage level is lower than a threshold voltage level; duringthe third time period, the first voltage increases from the load voltagelevel to the threshold voltage level.
 12. The system of claim 1 andfurther comprising: a frequency variation generator configured to outputa second control signal to the signal generator; wherein the signalgenerator uses the second control signal to vary the first frequency.13. The system of claim 12 wherein the frequency variation generatorincludes a clock randomizer.
 14. A system for providing frequencycontrol to a power converter, the system comprising: a first controllerconfigured to receive a load signal and generate a first control signal,the load signal indicating an output load for a power converter; acompensation system configured to receive an input signal for the powerconverter and generate a second control signal; a signal generatorconfigured to receive the first control signal and the second controlsignal and generates at least an output signal; wherein: the outputsignal is associated with a signal strength and a frequency; thefrequency is inversely proportional to a sum of a first time period, asecond time period, and a third time period; the signal strengthincreases with the time at a first slope during the first time period;the signal strength decreases with the time at a second slope during thesecond time period; the signal strength is constant with respect to thetime during the third time period; the first slope varies with the inputsignal within a signal range; the second slope varies with the inputsignal within the signal range.
 15. The system of claim 14 wherein thefirst slope is constant with respect to the load signal, and the secondslope is constant with respect to the load signal.
 16. The system ofclaim 14 wherein the first time period is constant with respect to theinput signal.
 17. The system of claim 16 wherein the first time periodis constant with respect to the load signal.
 18. The system of claim 14wherein the second time period is constant with respect to the inputsignal.
 19. The system of claim 18 wherein the second time period isconstant with respect to the load signal.
 20. The system of claim 14wherein the third time period varies with the load signal if the loadsignal is within a predetermined range.
 21. The system of claim 20wherein the third time period varies with the load signal if the loadsignal is within a predetermined range comprises: if the output load isless than a threshold load, the third time period increases with thedecreasing output load.
 22. The system of claim 21 wherein the thirdtime period equals zero if the load signal is not within thepredetermined range.
 23. The system of claim 14, and further comprisinga pulse-width-modulation generator configured to receive at least theoutput signal.
 24. The system of claim 23 wherein thepulse-width-modulation generator uses the output signal to perform aslope compensation for a feedback loop.
 25. The system of claim 24wherein the slope compensation is associated with a slope compensationratio, the slope compensation ratio being constant with respect to theinput signal.
 26. The system of claim 14 wherein the compensation systemcomprises: a sensing system configured to receive the input signal andgenerate a third control signal; a compensation controller configured toreceive the third control signal and output the second control signal.27. The system of claim 26 wherein the first control signal comprises aplurality of signals.
 28. A method for providing frequency control to apower converter, the method comprising: receiving a load signal, theload signal indicating an output load for a power converter; generatinga control signal in response to the load signal; processing informationassociated with the control signal; generating an output signal based onat least information associated with the control signal; wherein: theoutput signal is associated with a signal strength and a frequency; thefrequency is inversely proportional to a sum of a first time period, asecond time period, and a third time period; the signal strengthincrease with the time during the first time period; the signal strengthdecrease with the time during the second time period; the signalstrength is constant with respect to the time during the third timeperiod; the third time period varies with the load signal if the loadsignal is within a predetermined range.
 29. The method of claim 28wherein the third time period equals zero if the load signal is notwithin the predetermined range.
 30. A method for providing frequencycontrol to a power converter, the method comprising: receiving a loadsignal, the load signal indicating an output load for a power converter;generating a first control signal in response to the load signal;receiving an input signal for the power converter; generating a secondcontrol signal in response to the input signal; processing informationassociated with the first control signal and the second control signal;generating an output signal based on at least information associatedwith the first control signal and the second control signal; wherein:the output signal is associated with a signal strength and a frequency;the frequency is inversely proportional to a sum of a first time period,a second time period, and a third time period; the signal strengthincreases with the time at a first slope during the first time period;the signal strength decreases with the time at a second slope during thesecond time period; the signal strength is constant with respect to thetime during the third time period; the first slope varies with the inputsignal within a signal range; the second slope varies with the inputsignal within the signal range.
 31. The method of claim 30, and furthercomprising: performing a slope compensation for the power converter;wherein: the slope compensation is associated with a slope compensationratio; the slope compensation ratio is constant with respect to theinput signal.